Deciphering Sb–Au mineralization event in the Longshan deposit, South China: Linking sulfide geochemistry and hydrothermal alteration

Abstract

The Longshan is one slate-hosted Sb–Au deposit located in the Jiangnan orogenic belt, South China. It features two sets of mineralized quartz veins, striking in NE and NW directions, respectively. It remains unclear whether these veins are the products of one or two Au–Sb mineralizing event (s). In this study, geological investigation, TESCAN Integrated Mineral Analyzer (TIMA), coupled with high sensitivity laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) trace elements analyses of pyrite and arsenopyrite were performed to reveal the sulfides (pyrite and arsenopyrite) geochemistry, paragenesis and types of hydrothermal alteration. These results indicate that wallrock hydrothermal alteration is intensive for both vein sets, with the main alteration types being silicification, sericitization, sulfidation, and carbonatization. Detailed texture investigations show that there is an insignificant difference between these two sets of quartz veins, as zoning texture is well-developed for pyrite whereas arsenopyrite shows weak inhomogeneity. LA–ICP–MS trace elements concentrations also display similar ranges such as Au and Sb for both pyrite and arsenopyrite from both sets of veins. Complemented by the time gap between the ore-hosting structure (Late Triassic) and mineralization ages (Late Jurassic), we prefer to explain the formation of two sets quartz veins in the Longshan Sb–Au deposit as resulting from a single pulse of hydrothermal fluid infilling pre-existing structures, rather than from superimposed Sb–Au events. This interpretation explains the similarities in the nature of ore-forming fluids and processes.